Method of forming a fine pattern of ferroelectric film

ABSTRACT

For forming a fine pattern of ferroelectric film without using a resist, a solution containing polyalkoxide having ferroelectric components, as a base part, and functional groups to be activated when exposed to electromagnetic waves or corpuscular beams is used as a pattern forming agent. The pattern form agent is coated onto a substrate, and then electromagnetic or corpuscular beams are radiated thereover to form crosslinks between molecules in the agent. After the crosslinks are cured, the portions devoid of any crosslink and hence uncured are removed using a solvent. Then the molecules associated with the crosslinks remaining on the substrate are then heated to form a ferroelectric crystal.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to a method of forming a fine pattern offerroelectric film in the production of ferroelectric memories,ferroelectric sensors, superconductive devices, etc., and also to apattern forming agent suitable for use with such a formation method.

2. Description of the Related Art:

There is currently proposed, as a new semiconductor memory device, afilm-like ferroelectric memory which uses a material having apolarization inverting characteristic and being fusible in asemiconductor process. Since it is involatile, such a ferroelectricmemory may be used as an involatile memory and requires only a smallamount of voltage or current during reloading, thus realizing apractical involatile memory. In an ordinary semiconductor memory such asEPROM, since it is necessary to apply a more excessive current orvoltage than usual or to place the memory in an unusable condition inorder to clear the stored contents, a separate current source or voltagesource dedicated for clearing is needed. However in the proposedferroelectric memory, since the stored contents can be altered orcleared under normal conditions, it would be unnecessary to equip such aseparate current source or voltage source.

The ferroelectric material is widely used, in addition to theabove-described ferroelectric memories, in various ferroelectric sensorsand liquid crystal displays as well as superconductive devices andfunctional glass. In these applications, since a ferromagnetic film mustbe processed into a predetermined pattern, a method of forming a finepattern of ferroelectric film is important.

In conventional methods, a predetermined pattern is formed using thefollowing process. A ferroelectric film is formed by RF sputtering,whereupon the ferroelectric film is crystallized by fireing. Theresulting ferroelectric film is then processed by a fine-patterntreatment, such as chemical wet etching, ion milling such as physicaldry etching, or plasma etching using hydrogen chloride ortetrafluoromethane, for example. In wet etching, if the etching solutionis an alkaline solution such as of potassium hydroxide or sodiumhydroxide, an alkali-proof resist for the photosensitive film is formedby lithography, whereupon film portions other than a predeterminedpattern are removed using the etching solution. Thus a desired patternof ferroelectric film is obtained. If the etching solution is an acidicsolution such as of phosphoric acid, sulfuric acid, hydrocloric acid orfluoric acid, an acid-proof resist for the photosensitive film should beused.

However these conventional processes have the following problems:

(1) In wet etching, since it is an isotopic etching, the pattern to beleft over tends to become too narrow and/or the resist tends to peeloff, and so that fine patterning cannot be achieved.

(2) Though it is excellent for fine processing, ion milling step stillhas problems such as causing damage to the substrate and making itdifficult to select a suitable resist.

(3) Plasma etching has a very poor etching rate, is not suitable formass production and causes a lot of damage to the substrate, oftenbreaking the active wiring layer under the resist.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a method offorming a fine pattern of ferroelectric film In simple steps, and toprovide a pattern forming agent suitable for use in such a method.

A more specific object of the invention is to provide a method and anagent for forming a fine pattern of ferroelectric film without using anyresist.

According to a first aspect of the invention, there is provided apattern forming agent for use in forming a fine pattern of ferroelectricfilm, wherein the pattern forming agent is a solution containing apolyalkoxide (hereinafter called "the photo active polymer") havingferroelectric components, as a base part, and functional groups whichcan be activated by exposure to electromagnetic waves or corpuscularbeams. The pattern forming agent is coated onto a substrate, andelectromagentic waves or corpuscular beams are then radiated over thecoated substrate to form crosslinks between molecules in the agent,whereupon the photo-active-polymer layer portions devoid of crosslinksare removed using a solvent. The molecules associated with thecrosslinks left over on the substrate are then processed with a thermaltreatment to form a ferroelectric crystal.

According to a second aspect of the invention, there is provided amethod for forming a fine pattern of ferroelectric film, comprising thesteps of: coating onto a substrate the photo-active-polymer-containingsolution (the first pattern forming agent of the invention); drawing acircuit pattern on the substrate by radiating the electromagnetic wavesor the corpuscular beams along the circuit pattern (by exposing thecircuit pattern to the electromagnetic waves or the corpuscular beams);developing the circuit pattern on the substrate by soaking the radiatedsubstrate in a predetermined solvent; and fireing the developed circuitpattern.

In this pattern forming method, the photo-active-polymer-containingsolution (the first pattern forming agent of the invention) is coatedonto the substrate.

Then in the drawing (exposing) step, the electromagnetic waves orcorpuscular beams (hereinafter called "electromagnetic waves") areradiated over the coated substrate along a desired circuit pattern.

At the agent areas exposed to the electromagnetic waves, the functionalgroups of the photo active polymer contained in the pattern formingagent are activated to produce various activated molecules. Since theseactivated molecules attack unsaturated bonds of the functional groups ofanother metal-alkoxide polymer to polymerize therewith, crosslinks areformed between the metal-alkoxide polymers contained in the patternforming agent. Upon formation of the crosslinks between the polymers,the pattern forming agent is cured so as to be insoluble in virtuallyany solvent. Consequently, when the coated substrate is soaked in asuitable known solvent after having been exposed to the electromagneticwaves along a desired circuit pattern, the unexposed portions are thenwashed away while only the exposed portions remain on the substrate.

In the fireing step, when the circuit pattern remaining on the substrateis fired at a temperature of about 600° to 800° C., the organicfunctional groups of the high polymer compound constituting the circuitpattern are removed while only the ferroelectric components remain inthe circuit pattern and are then crystallized under heat. As a result, afine pattern ferroelectric film has been formed along the desiredcircuit pattern.

The photo active polymer is preferably a metal-alkoxide polymer havingfunctional groups with unsaturated bonds and atoms other than of Carbonor Hydrogen (hereafter known as heteroatoms). The metals of themetal-alkoxide are exemplified by Pb, Zr, Ti, Ba and La, which arematerials such as of PZT or PLZT.

In the above-mentioned pattern forming method, if the photo activepolymer is a metal-alkoxide polymer having functional groups withunsaturated bonds, a solution containing the metal-alkoxide polymers iscoated onto the substrate, and the coated substrate is exposed to theelectromagnetic waves. At the exposed areas, the unsaturated bonds ofthe functional groups of the metal-alkoxide polymer contained in thepattern forming agent are broken to generate radicals. By the well-knownradical reaction, these radicals attack the unsaturated bonds offunctional groups of another metal-alkoxide polymer to polymerizetherewith. Accordingly the exposed areas produce new bonds between themetal-alkoxide polymers to form a network polymer. Then the portionsformed with the network polymer are cured so as to become insoluble invirtually any solvent. Therefore, in the developing step, when theexposed substrate is soaked in a predetermined solvent, the exposedportions are left over in a desired circuit pattern on the substrate.

In the fireing step, a fine pattern of ferroelectric film is formedalong the desired circuit pattern.

The photo active polymer should by no means be limited to ametal-alkoxide polymer having functional groups with unsaturated bondsand may be a metal-alkoxide polymer with functional groups having anunstable structure such as α,β-unsaturated carbonyl compounds. For thereason described above, the metals of the metal-alkoxides areexemplified by Pb, Zr, Ti, Ba and La, which are materials such as of PZTor PLZT.

In the pattern forming method, if the photo active polymer is ametal-alkoxide polymer with functional groups having an unstablestructure, a solution containing the metal-alkoxide polymers is coatedonto the substrate, and the coated substrate is exposed toelectromagnetic waves. At the exposed areas, this metal-alkoxide polymercontained in the pattern forming agent is broken more easily than theunsaturated bonds of the functional groups of the metal-alkoxide polymerto generate radicals. These radicals attack the unsaturated bonds offunctional groups of another metal-alkoxide polymer to polymerizetherewith. Accordingly the exposed areas produce new bonds between themetal-alkoxide polymers to form a network polymer. Then the portionsformed with the network polymer are cured so as to become insoluble invirtually any solvent. Therefore, in the developing step, when theexposed substrate is soaked in a predetermined solvent, the exposedportions are left over in a desired circuit pattern on the substrate.

In the fireing step, a fine pattern of ferroelectric film is formedalong the desired circuit pattern.

As a second pattern forming agent, a photo active polymer (polyalkoxidehaving ferroelectric components and functional groups to be activatedwhen exposed to electromagnetic waves or corpuscular beams), and a photoactive compound to be activated, when exposed to electromagnetic wavesor corpuscular beams, so as to form crosslinks in the alkoxide polymerare dissolved in a solvent.

This photo active compound sensitive to electromagnetic waves orcorpuscular beams to form crosslinks between polymers is preferably anaromatic bis-azide compound.

The method using the second pattern forming agent comprises coating ontothe substrate a solution containing the photo active polymer and thephoto active compound (the second pattern forming agent), drawing acircuit pattern on the substrate by radiating the electromagnetic wavesor the corpuscular beams along the circuit pattern, developing thecircuit pattern on the substrate by soaking the radiated substrate in apredetermined solvent, and fireing the developed circuit pattern.

According to this pattern forming method, in the coating step, thesolution (the second pattern forming agent) containing the photo activepolymer and the photo active compound is coated over the substrate.

Then in the drawing (exposing) step, the substrate coated with the mixedsolution is exposed to electromagnetic waves or corpuscular beams alonga desired circuit pattern.

In the exposed areas of the second pattern forming agent, the functionalgroups of the photo active polymer and those of the photo activecompound are respectively activated to generate various activatedmolecules. Since these activated molecules serve as a crosslinking agentto attack the unsaturated bonds of the functional groups of anothermetal-alkoxide polymer to polymerize therewith, crosslinks are formedbetween the metal-alkoxide polymers of the pattern forming agent toproduce a network polymer. Having this network polymer, such portions ofthe pattern forming agent are then cured so as to be insoluble in anysolvent. Therefore, by washing the whole of the exposed substrate with asuitable solvent, it is possible to leave only the exposed portions onthe substrate. In the developing step, the exposed substrate is soakedin a predetermined solvent to wash away the unexposed portions while theexposed portions in a desired circuit pattern remain on the substrate.

Then in the fireing step, when the circuit pattern remaining on thesubstrate is fired at a temperature of about 600° to 800° C., theorganic functional groups of the high polymer compound constituting thecircuit pattern are removed while only the ferroelectric components areleft in the circuit pattern and are then crystallized under heat. As aresult, a fine pattern ferroelectric film has been formed along thedesired circuit pattern.

Since the photo active compound is more sensitive to the electromagneticwaves than the photo active polymer, the second pattern forming agenthas a better response to the electromagnetic waves and hence can becured, when exposed to the electromagnetic waves, more easily comparedto the first pattern forming agent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing a succession of processing steps whenproducing a first pattern forming agent, according to this invention, tobe used in forming a fine pattern of ferroelectric film;

FIG. 2 shows one stage of operation (the pattern-forming-agent coatingstep) of a fine-pattern forming method according to the invention in aconcrete form;

FIG. 3 shows another stage of operation (the developing step and thefireing step) of the fine-pattern forming method;

FIG. 4 is a flow diagram showing a succession of processing steps whenproducing a second pattern forming agent according to the invention, anda succession of processing steps of a pattern forming method using thesecond pattern forming agent;

FIG. 5 is a flow diagram showing a succession of processing steps whenproducing a third pattern forming agent; and

FIG. 6 shows the reaction mechanism in which crosslinks of the thirdpattern forming agent are formed.

DETAILED DESCRIPTION

Preferred examples of a method for forming a fine pattern offerroelectric film according to this invention will now be describedwith reference to the accompanying drawings.

Fine-Pattern Forming Method

In this method, a pattern forming agent is a solution containing apolyalkoxide (the photo active polymer) having ferroelectric components,as a base part, and functional groups to be activated when exposed toelectromagnetic waves or corpuscular beams. The pattern forming agent iscoated onto a substrate, and electromagnetic waves or corpuscular beamsare then radiated over the coated substrate to form crosslinks betweenmolecules in the agent, whereupon the photo-active-polymer layerportions devoid of crosslinks are removed using a solvent. The moleculesassociated with the crosslinks left on the substrate are then processedwith thermal treatment to form a ferroelectric crystal.

FIG. 1 is a flow diagram showing a succession of processing steps of thepattern forming method.

In this embodiment, in the coating step S101, the pattern forming agentis coated onto the substrate. Then in the drawing (exposing) step S102,the coated substrate is exposed to light (or electromagnetic waves)along a predetermined pattern, whereupon in the developing step S103,the exposed substrate is soaked in a predetermined solvent to remove theunexposed portions of the pattern forming agent on the substrate. Atthat time, since the pattern forming agent at the exposed areas iscured, the pattern forming agent at the unexposed areas is removed whileonly the pattern forming agent in the predetermined pattern remains onthe substrate. In the fireing step S104, the predetermined pattern ofthe pattern forming agent remaining on the substrate is treated withheat. During the fireing step, the organic functional groups of thepolyalkoxide are removed while the ferroelectric components are left onthe substrate and are then crystallized to produce a ferroelectric(e.g., PZT or PLZT) having a perovskite structure. In the drawing(exposing) step S102, the substrate may be exposed to electromagneticwaves other than light, or to other corpuscular beams (e.g., electronrays or neutron rays).

FIG. 2 shows one stage of operation of the pattern forming method inconcrete form.

In this pattern forming method, for obtaining a polyalkoxide havingpredetermined metals, various kinds of metal-alkoxides as material aredissolved in alcohol to prepare a starting solution. The predeterminedmetals are exemplified by Pb, Zr, Ti, Ba and La, which are materialssuch as PZT or PLZT. When water as a catalyst is added to this startingsolution, a hydrolysis reaction and condensation reaction respectivelyexpressed by the following reaction formulas (1) and (2) take place toproduce polyalkoxide. This method is generally known as the sol-gelmethod. The polyalkoxide to be used in the pattern forming method may beproduced easily using this known sol-gel method.

SOL-GEL Method

    M(OR).sub.n +nH.sub.2 ----M (OH).sub.N +nHOR               (1)

    xM(OH).sub.n ----(MO.sub.n/2).sub.n +(xn/2)H.sub.2 O       (2)

In this embodiment, the solution containing polyalkoxide is coated ontoa platinum substrate 11 (the coating step) by spinning or soaking, asshown in FIG. 2. By spin coating, it is possible to coat the solutionover the substrate uniformly so that a film having a uniform thicknesscan be formed. The thickness of the film formed in the coating step isabout 400 to 800 angstrom; and the coating method used may be selecteddepending on the thickness.

FIG. 3 shows the developing steps and the fireing step of the patternforming method in a concrete form.

As shown in FIG. 3, light is radiated onto the solution 13, which iscoated on the substrate 11, along a predetermined pattern by a lightradiating means 15. At that time, since a light polymerization reactiontakes place at the exposed areas, the solution 13 is cured along apredetermined pattern. Upon exposure to light, unsaturated bondscontained in the high-polymeric compound are partly broken to generateradicals. As these radicals attack other polyalkoxide, bonds aregenerated there to produce a high polymer of a large molecular mass. Thelarger the molecular mass, the more its viscosity increases. Utilizingthis viscosity difference, it is possible to remove the areas other thanthe areas exposed to laser beams by a conventional means, such as a CO₂laser or an excimer laser. The coated substrate 11 may be exposed toelectron rays, X-rays or ultraviolet rays.

Subsequently, the solution 13 other than the exposed portions is removedfrom the substrate 11 by a solvent which dissolves the polyalkoxide. Inthis embodiment, the solution 13 is removed from selected areas using anorganic solvent of an aromatic group such as benzene or toluene; thatis, even when the solution 13 is removed from the substrate 11, thecured portions 13P cured by light radiation remains on the substrate 11.Since light radiation is given along a predetermined pattern, the curedportion 13P in the predetermined pattern is formed on the substrate 11.

Then when the cured portion 13P is treated with heat, a fine pattern 13Qof ferroelectric film is formed. In the polyalkoxide polymerized bythermal treatment of 600° to 800° C., organic portions are removed whileferroelectric components are left on the substrate. With continuedheating, the remaining components are crystallized to assume aperovskite structure so that a fine pattern 13Q of ferroelectric filmsuch as PZT and PLZT is formed.

In the foregoing pattern forming methods, resistless fine processing canbe achieved, and it is possible to minimize damage caused during dryetching, thus simplifying the process and reducing the cost ofproduction.

Various pattern forming agents suitable for use in the pattern formingmethod will now be described.

Fine-Pattern Forming Agent

(FIRST EXAMPLE)

In this example, the photo active polymer is a metal-alkoxide polymercontaining functional groups with unsaturated bonds, as expressed by thefollowing formula (3). The feature of this polymer is that it hasunsaturated bonds and ferromagnetic components (such as PZT or PLZT),which generate radicals to cause polymerization and hence solidificationby light radiation. When the polymerized molecules are heated, theorganic functional portions are removed and, at the same time,crystallization occurs to form a ferroelectric. ##STR1## where R₁represents an alkyl group such as --CH₃ or --C₂ H₅, R₂ represents anunsaturated functional group such as --CH═CH₂, R₃ represents an arylgroup such as benzine, toluene, and M represents a metal-atom selectedfrom the group consisting of at least Pb, Zr, Ti, La and Ba.

The polyalkoxide as expressed by the formula (3) can be easily producedusing the known sol-gel method. Various kinds of metal-alkoxides asmaterials are dissolved in alcohol to prepare a starting solution. Whenwater as a catalyst is added to this starting solution, hydrolysisreaction and condensation reaction respectively expressed by thefollowing reaction formulas (1) and (2) take place to produce thepolyalkoxide as expressed by the formula (3).

As already described above, the metal-alkoxide as expressed by theformula (3) is coated onto the substrate 11, and electromagnetic waveradiation is applied thereover in a predetermined pattern to generateradicals to cause a well-known chain reaction to form crosslinks betweenmolecules for solidification. Then the not cured portions removed by asolvent while only the cured portions remain on the substrate. The curedportions are treated with heat to remove and crystallize the organicfunctional portions concurrently. Thus it is possible to form a desiredfine pattern of ferroelectric film on the substrate 11, without usingany resist.

A polymerization retardant such as diethanol amine and a sensitizer suchas 1-nitropylene or 1,8-dinitropylene may be added to the solution 13 asrequired. To improve the sensitivity to electromagnetic waves, anaromatic bisazide compound may be added to the solution 13 to formcrosslinks in the polyalkoxide.

(SECOND EXAMPLE)

A polymer (base polymer) to be used as the material of a photo activepolymer in this example is expressed by the following formula. ##STR2##

This base polymer contains metal-atoms selected from the groupconsisting of at least zirconium, lead, titan and lanthanum, which areferromagnetic materials of PZT and PLZT. When the photo active polymerderived from the base polymer is treated at high temperature, organiccomponents in molecules are removed by oxidation so that only componentsforming a ferroelectric film such as PZT remain on the substrate. Withcontinued high-temperature treatment, the remaining ferroelectriccomponents are progressively crystallized into a perovskite structurecomposed of fine crystal particles.

FIG. 4 is a flow diagram showing a succession of processing steps whenproducing a second pattern forming agent according to the invention, anda succession of processing steps of a pattern forming method using thesecond pattern forming agent.

Firstly, metal-butoxides having 1-hydroxypropyl groups in molecules aremixed up, and then diethanol amine as a polymerization retardant isadded to the mixture. Toluene and isopropanol are added to the resultingmixture to obtain a solution containing the metal-butoxide. When wateris added to the solution, hydrolysis takes place to produce butanol andmetal hydroxides, whereupon metal hydroxides cause a polymerizationreaction with one another to produce the base polymer.

In this example, the base polymer is a polyalkoxide containing theabove-mentioned metal elements as pivot atoms, and organic functionalgroups having alcoholic hydroxyl groups are C-bonded with the respectivepivot atoms. When various photo active compounds expressed by thefollowing formulas (5) are mixed with the solution containing this basepolymer, a condensation reaction will soon take place to produce a photoactive polymer as expressed by the formula (6). This photo activepolymer is an unstable compound containing α,β-unsaturated carbonyl, andthe unsaturated bonds are apt to break when exposed to electromagneticwaves. Upon radiation of electromagnetic waves to the photo activepolymer, the unsaturated bonds are broken and, at the same time, bondsoccur to form crosslinks between molecules. As the molecular mass isthus increased due to the crosslinks, the viscosity of the fine-patternforming agent containing the photo active polymer will be increased.Therefore it is possible to separate the exposed portions and theunexposed portions from one another by conventional technology. ##STR3##

In the second example, as the photo active polymer as expressed by theformula (6) is mixed in a suitable solvent such as acetone, the secondfine-pattern forming agent is obtained.

Since the reaction is retarded by diethanol amine previously added tothe reaction mixture, it is possible to adjust the molecular length ofthe base polymer and the molecular length of the photo active polymer;that is, it is possible to adjust the viscosity of the fine-patternforming agent containing these polymers. If its viscosity is too high,such an agent is not suitable for the fine-pattern forming method ofthis invention. This is true partly because such a highly viscous agentis not suitable for being coated onto the substrate at a constanttemperature and also because it is not suitable for being removed fromthe areas outside the predetermined pattern. A sensitizer such as1-nitropylene or 1,8-dinitropylene may be added as required.

The second fine-pattern forming agent is first stirred so as to have auniform structure, whereupon in the coating step S201 it is coateduniformly over the substrate. In this example, spin coating is used toachieve uniform coating. After being dried for a while, the coatedsubstrate is exposed at selected areas to ultraviolet rays, X-rays orcorpuscular beams (hereinafter also called "electromagnetic waves").

When this fine-pattern forming agent is exposed to electromagneticwaves, crosslinks are formed between molecules in the exposed areaswhere the molecules become larger than those at the crosslink-freeareas. Therefore at only the crosslinked areas, the fine-pattern formingagent is remarkedly increased in viscosity and becomes hard. Once it hasbecome hard, the fine-pattern forming agent becomes insoluble invirtually any solvent. Therefore only the portions free of thecrosslinking reaction can be removed while the other portions treatedwith the crosslinking reaction can remain on the substrate. If lightradiation takes place along a predetermined pattern, only the portionsin the predetermined pattern can remain on the substrate. In thedeveloping step S204, light radiation is done along a predeterminedpattern. As the crosslinking reaction occurs along a predeterminedpattern of areas, only the fine-pattern forming agent at the exposedareas becomes markedly lower in fluidity and hence hard so that it willbecome insoluble in virtually any organic solvent. In the developingstep S204, acetone is used as a solvent, and the fine-pattern formingagent at the unexposed areas is removed while the exposed portionsremain on the substrate (S205). In the developing step S204, the exposedportions can be removed with adjustable ease by adjusting the quantityof diethanol amine previously added in the group as a polymerizationretardant.

Subsequently, in the heating step S206, the fine-pattern forming agentis dried at 300° to 500° C. and, in the fireing step S207, it undergosthermal treatment. During the fireing step S207, when the fine-patternforming agent is heated at 600° to 700° C., the organic functionalgroups will be oxidized so as to be removed from the crosslinked highpolymer compound, and at the same time, the residual metal-alkoxideportions are crystallized to have a perovskite structure.

In this example, light radiation is applied to the fine-pattern formingagent along a predetermined pattern, whereupon the agent at thepredetermined pattern is removed based on the viscosity differencebetween the exposed areas and the unexposed areas. Thus it is possibleto form a fine pattern of ferroelectromagnetic film on the substratewithout using any resist.

As described above, the fine-pattern forming agent of this example canbe produced without using any resist, minimizing possible damage duringdry etching and simplifying the process.

(THIRD EXAMPLE)

A fine-pattern forming agent of this example contains, in addition to apolyalkoxide having ferroelectric components and unsaturated bonds, anaromatic bis-azide compound which assists in forming crosslinks betweenmolecules of the polyalkoxide. Electromagnetic waves are radiated to thefine-pattern forming agent to form crosslinks between the molecules, andthen only the crosslinked molecules remain on the substrate and arethermally treated to produce a ferroelectric crystal. Thus in thisexample, the polyalkoxide having ferroelectric components andunsaturated bonds is a photo active polymer, and the aromatic bis-azidecompound is a photo active compound; the photo active compound is addedto the photo active polymer, and the resulting mixture is dissolved in asolvent to form this fine-pattern forming agent.

The structure of the photo active polymer to be used in this example isexpressed by the following formula: ##STR4## where R₁ represents analkyl group such as --CH₃ or --C₂ H₅, R₂ represents an unsaturatedfunctional group such as --CH═CH₂, R₃ represents an aryl group such asbenzene, toluene, and M represents a metal-atom selected from the groupconsisting of at least Pb, Zr, Ti, La and Ba.

The photo active polymer contains metal-atoms selected from the groupconsisting of at least zirconium, lead, titan and lanthane, which areferroelectric materials such as of PZR or PLZT. In this example, afterthe organic function groups have been removed, only the components forforming a ferroelectric film such as PZT will be left on the substrate.To oxidize and remove the organic components in molecules of the photoactive polymer, the photo active polymer is treated at high temperature.With continued treatment at high temperature after the organiccomponents are removed with only the ferroelectric components remaining,it will undergo crystallization to produce a perovskite structure whichhas a domain voluntarily polarized in a predetermined direction and iscomposed of fine crystal particles.

The photo active polymer is a polyalkoxide having the above-describedmetal-atoms as pivot atoms with which the organic functional groups arebonded, there being contained in the organic functional groupsunsaturated bonds. The polymer and an aromatic bis-azide compound asexpressed by the following formula (8) are mixed in a suitable solventto form a fine-pattern forming agent of this example.

FIG. 5 shows the manner in which the third fine-pattern forming agent ofthis example, and also the manner in which a fine pattern offerroelectric film is formed using the third fine-pattern forming agent.

Metal-butoxide having unsaturated bonds in molecules is mixed with thephoto active polymer, and diethanol amine as a polymerization retardantis added to the resulting mixture. Further, toluene and isopropanol areadded to this mixture to obtain a solution containing the metalbutoxide. When water is added to this solution, hydrolysis will takeplace to produce normal butanol and metal hydroxides, whereupon metalhydroxides soon cause a polymerization reaction with one another toproduce the photo active polymer.

Since the reaction is retarded by diethanol amine previously added tothe reaction mixture, it is possible to adjust the molecular length ofthe base polymer and the molecular length of the photo active polymer;that is, it is possible to adjust the viscosity of the fine-patternforming agent containing these polymers. If its viscosity is too high,such an agent is not suitable for the fine-pattern forming method ofthis invention. This is true partly because such a highly viscous agentis not suitable for being coated onto the substrate at a constanttemperature and also because it is not suitable for being removed fromthe areas other than a predetermined pattern.

When an aromatic bisazide compound as expressed by the following formula(8) is added to the resulting solution having a predetermined viscosity,a fine-pattern forming agent of this example is formed. Further, asensitizer (such as 1-nitropylene or 1,8-dinitropylene) as shown in FIG.5 is added. ##STR5##

The resulting mixture is stirred so as to have a uniform structure,whereupon in the coating step S201 it is coated uniformly over thesubstrate. In this example, spin coating is used to achieve uniformcoating. After being dried for a while, the coated substrate is exposedat selected areas to ultraviolet rays, X-rays or corpuscular beams(hereinafter also called "electromagnetic waves").

When electromagnetic waves are radiated to this mixture, a crosslinkingreaction will take place as shown in FIG. 6. Specifically, when thearomatic bis-azide compound is exposed to electromagnetic waves,nitrogen gas will become free and, at the same time, monovalent excitednitrogen will be produced in the molecule. The monovalent nitrogen thenattacks the unsaturated bonds in the polyalkoxide molecule to cleavethem for addition. Since the bis-azide compound has two azide groups,the addition reaction will take place at opposite ends of the molecule.So when a plurality of the photo active polymers are respectivelyattacked, crosslinks will be formed between these molecules. Since thecrosslinked portion becomes a high polymer larger than that of thecrosslink-free portion, only the crosslinked portion will be increasedin visicosity and hence lower in fluidity so that such portions willbecome insoluble in virtually any organic solvent. Therefore, using aconventional organic solvent, it is possible to remove only the portionsfree from the crosslinking reaction, with the crosslinked portionsremaining on the substrate.

In the lithographing step S304, light radiation takes place along apredetermined pattern. The crosslinking reaction occurs along thispattern so that only the exposed portions will become cured so as to beinsoluble in virtually any solvent. In the removing step S305, usingbenzene as a solvent, the fine-pattern forming agent at the unexposedareas is removed and, at the same time, only the exposed portions remainon the substrate. In the removing step S305, the exposed portions can beremoved with adjustable ease by adjusting the quantity of diethanolamine previously added to the reaction mixture as a polymerizationretardant.

Subsequently, in the heating step S307, the fine-pattern forming agentis dried at 300° to 500° C. and, in the fireing step S308, it undergoesthermal treatment. During the fireing step S308, when the fine-patternforming agent is heated at 600° to 700° C., the organic functionalgroups will be oxidized so as to be removed from the crosslinked highpolymer compound, and at the same time, the residual metal-alkoxideportions are crystallized to have a perovskite structure.

In this example, light radiation is given to the fine-pattern formingagent along a predetermined pattern, whereupon the agent at thepredetermined pattern is removed based on the viscosity differencebetween the exposed areas and the unexposed areas. Thus it is possibleto form a fine pattern of ferroelectromagnetic film on the substratewithout using any resist.

As described above, the fine-pattern forming agent of this example canbe produced without using any resist, minimizing possible damage duringdry etching and simplifying the process.

What is claimed is:
 1. A method for forming a fine pattern offerroelectric film, comprising the steps of:(a) coating onto a substratea pattern forming agent for forming the fine pattern of ferroelectricfilm, said pattern forming agent being a solution containing apolyalkoxide having ferroelectric components in the backbone structureof the polyalkoxide, and functional groups attached to the backbonestructure of the polyalkoxide to be activated when exposed toelectromagnetic waves or corpuscular beams; (b) drawing a circuitpattern on the substrate by radiating electromagnetic waves orcorpuscular beams along the circuit pattern; (c) developing the circuitpattern on the substrate by soaking the radiated substrate in an organicsolvent having an aromatic group; and (d) firing the developed circuitpattern.
 2. A method for forming a fine pattern of ferroelectric film,comprising the steps of:(a) coating onto a substrate a pattern formingagent for forming the fine pattern of ferroelectric film, said patternforming agent being a solution containing a polyalkoxide havingferroelectric components in the backbone structure of the polyalkoxide,and functional groups attached to the backbone structure of thepolyalkoxide to be activated when exposed to electromagnetic waves orcorpuscular beams, said polyalkoxide being a metal-alkoxide polymer withunsaturated bonds; (b) drawing a circuit pattern on the substrate byradiating electromagnetic waves or corpuscular beams along the circuitpattern; (c) developing the circuit pattern on the substrate by soakingthe radiated substrate in an organic solvent having an aromatic group;and (d) firing the developed circuit pattern.
 3. A method for forming afine pattern of ferroelectric film, comprising the steps of:(a) coatingonto a substrate a pattern forming agent for forming the fine pattern offerroelectric film, said pattern forming agent being a solutioncontaining a polyalkoxide having ferroelectric components in thebackbone structure of the polyalkoxide, and functional groups attachedto the backbone structure of the polyalkoxide to be activated whenexposed to electromagnetic waves or corpuscular beams, said polyalkoxidebeing a metal-alkoxide polymer having the following formula: ##STR6##where R₁ represents an alkyl group, R₂ represents an unsaturatedfunctional group, R₃ represents an aryl group and M represents ametal-atom selected from the group consisting of Pb, Zr, Ti, La, Ba, Bi,Si, Li and Nb; (b) drawing a circuit pattern on the substrate byradiating electromagnetic waves or corpuscular beams along the circuitpattern; (c) developing the circuit pattern on the substrate by soakingthe radiated substrate in an organic solvent having an aromatic group;and (d) firing the developed circuit pattern.
 4. A method for forming afine pattern of ferroelectric film, comprising the steps of:(a) coatingonto a substrate a pattern forming agent for forming the fine pattern offerroelectric film, said pattern forming agent being a solutioncontaining a polyalkoxide having ferroelectric components in thebackbone structure of the polyalkoxide, and functional groups attachedto the backbone structure of the polyalkoxide to be activated whenexposed to electromagnetic waves or corpuscular beams, said polyalkoxidebeing a metal-alkoxide polymer having the following formula: ##STR7##where M represents a metal-atom which is a ferroelectric compound, R₁represents an alkyl group, and R₂ represents an alkyl group containingheteroatoms; (b) drawing a circuit pattern on the substrate by radiatingelectromagnetic waves or corpuscular beams along the circuit pattern;(c) developing the circuit pattern on the substrate by soaking theradiated substrate in an organic solvent having an aromatic group; and(d) firing the developed circuit pattern.
 5. A method for forming a finepattern of ferroelectric film, comprising the steps of:(a) coating ontoa substrate a pattern forming agent for forming the fine pattern offerroelectric film, said pattern forming agent being a solutioncontaining a polyalkoxide having ferroelectric components in thebackbone structure of the polyalkoxide, and functional groups attachedto the backbone structure of the polyalkoxide to be activated whenexposed to electromagnetic waves or corpuscular beams, said polyalkoxidebeing a metal-alkoxide polymer having the following formula: ##STR8##(b) drawing a circuit pattern on the substrate by radiatingelectromagnetic waves or corpuscular beams along the circuit pattern;(c) developing the circuit pattern on the substrate by soaking theradiated substrate in an organic solvent having an aromatic group; and(d) firing the developed circuit pattern.
 6. A method for forming a finepattern of ferroelectric film, comprising the steps of:(a) coating ontoa substrate a pattern forming agent for forming the fine pattern offerroelectric film, said pattern forming agent being a solutioncontaining i) a polyalkoxide having ferroelectric components in thebackbone structure of the polyalkoxide, and functional groups attachedto the backbone structure of the polyalkoxide to be activated whenexposed to electromagnetic waves or corpuscular beams, and ii) a photoactive compound to be activated, when exposed to electromagnetic wavesor corpuscular beams, so as to form crosslinks in said polyalkoxide; (b)drawing a circuit pattern on the substrate by radiating electromagneticwaves or corpuscular beams along the circuit pattern; (c) developing thecircuit pattern on the substrate by soaking the radiated substrate in anorganic solvent having an aromatic group; and (d) firing the developedcircuit pattern.
 7. A method for forming a fine pattern of ferroelectricfilm, comprising the steps of:(a) coating onto a substrate a patternforming agent for forming the fine pattern of ferroelectric film, saidpattern forming agent being a solution containing i) a polyalkoxidehaving ferroelectric components in the backbone structure of thepolyalkoxide, and functional groups attached to the backbone structureof the polyalkoxide to be activated when exposed to electromagneticwaves or corpuscular beams, and ii) a photo active compound to beactivated, when exposed to electromagnetic waves or corpuscular beams,so as to form crosslinks in said polyalkoxide, said polyalkoxide being ametal-alkoxide polymer with unsaturated bonds, said photo activecompound being an aromatic bisazide compound; (b) drawing a circuitpattern on the substrate by radiating electromagnetic waves orcorpuscular beams along the circuit pattern; (c) developing the circuitpattern on the substrate by soaking the radiated substrate in an organicsolvent having an aromatic group; and (d) firing the developed circuitpattern.
 8. A method for forming a fine pattern of ferroelectric film,comprising the steps of:(a) coating onto a substrate a pattern formingagent for forming the fine pattern of ferroelectric film, said patternforming agent being a solution containing i) a polyalkoxide havingferroelectric components in the backbone structure of the polyalkoxide,and functional groups attached to the backbone structure of thepolyalkoxide to be activated when exposed to electromagnetic waves orcorpuscular beams, and ii) a photo active compound to be activated, whenexposed to electromagnetic waves or corpuscular beams, so as to formcrosslinks in said polyalkoxide, said polyalkoxide being ametal-alkoxide polymer with unsaturated bonds, said metal-alkoxidepolymer being expressed by the following formula: ##STR9## wherein R₁ isan alkyl group, R₂ is an unsaturated functional group, R₃ is an arylgroup, M is a metal-atom which is a material ferroelectric compound, andsaid photo active compound being an aromatic bisazide compound expressedby the following formula: ##STR10## (b) drawing a circuit pattern on thesubstrate by radiating electromagnetic waves or corpuscular beams alongthe circuit pattern; (c) developing the circuit pattern on the substrateby soaking the radiated substrate in an organic solvent having anaromatic group; and (d) firing the developed circuit pattern.
 9. Amethod according to claim 7, wherein said solvent used in saiddeveloping step is benzene.
 10. A method according to claim 8, whereinsaid solvent used in said developing step is benzene.
 11. A method forforming a fine pattern of ferroelectric film according to claim 3,wherein said metal-atom of said pattern forming agent which is amaterial ferroelectric compound is selected from the group consisting ofPb, Zr, Ti, La and Ba.
 12. A method for forming a fine pattern offerroelectric film according to claim 4, wherein said metal-atom of saidpattern forming agent which is a material ferroelectric compound isselected from the group consisting of Pb, Zr, Ti, La, Ba, Bi, Si, Li andNb.
 13. A method for forming a fine pattern of ferroelectric filmaccording to claim 8, wherein said metal-atom of said pattern formingagent which is a material ferroelectric compound is selected from thegroup consisting of Pb, Zr, Ti, La, Ba, Bi, Si, Li and Nb.
 14. A methodaccording to claim 3, wherein said organic solvent used in saiddeveloping step (c) is benzene.
 15. A method according to claim 4,wherein said organic solvent used in said developing step (c) isbenzene.
 16. A method according to claim 3, wherein said organic solventused in said developing step (c) is toluene.
 17. A method according toclaim 4, wherein said organic solvent used in said developing step (c)is toluene.